CN111526966A - Laser processing apparatus and method - Google Patents

Abstract

The invention relates to a device and the use thereof for laser welding. A laser welding apparatus includes: at least one first laser device (30) each providing at least one first optical feed fiber (32) with a first laser beam; at least one second laser device (31) each providing at least one second optical feed fiber (33) with a second laser beam; a tool for generating a composite laser beam comprising a first output laser beam and a second output laser beam (2) for welding a workpiece (21); wherein the first output laser beam has a circular cross-section and the second output laser beam (2) has a ring-like shape concentric with the first output laser beam. The second laser device (31) is a fiber laser device or a fiber coupled laser device. The apparatus is configured to form a second output laser beam (2) based on at least the second laser beam, and the second output laser beam (2) comprises a first wavelength and a second wavelength having a difference of at least 10 nanometers, or the second output laser beam (2) has a spectral width of at least 10 nanometers.

Description

Laser processing device and method

technical field

The present invention relates to a laser processing apparatus and method. In particular, the present invention relates to the welding of materials processed by a laser.

Background technique

When welding metals with a laser beam, the laser beam is usually condensed into a 100-500µm spot by a condenser lens to increase the energy density and instantaneously heat the workpiece to a temperature of 1500°C or above, causing the workpiece to melt. At the same time, auxiliary gas can be fed to prevent oxidation of the molten metal. Laser beams in the one-micrometer band from solid-state lasers or fiber lasers achieve very high light energy intensities and absorption rates on metal parts compared to laser beams in the ten-micrometer band of _CO2 lasers. However, if a one-micron band laser beam with a Gaussian beam is used to cut a mild steel plate workpiece with an oxygen assist gas, the melting width on the top surface of the workpiece is unnecessarily widened and kerf control is impaired. In addition, spontaneous combustion that degrades the quality of the laser cut may occur.

It is known in the art of laser material processing to use a ring-shaped laser beam, which provides an intensity distribution that can be described as having a ring-shaped or "doughnut"-like shape. It has been observed that cutting of a given thickness of metal can be performed at a much lower power level when using a donut beam rather than a more conventional beam profile, which can improve cutting speed and quality.

US8781269 discloses various arrangements for directing a laser beam into a multi-clad fiber to generate different beam distribution characteristics of an output laser beam, wherein the input laser beam is selectively coupled into an inner fiber core or an outer annular core .

This material processing application seeks to maximize the brightness of the laser beam. Brightness is defined as power per unit solid angle and unit area. As an example of the importance of brightness, by increasing the brightness of the laser beam, processing speed or material thickness can be increased. High brightness laser beams can be obtained from, for example, fiber lasers and thin disk lasers. Direct diode lasers have also continued to improve in brightness, but it is true that commercial direct diode lasers for materials processing have not yet achieved the brightness of fiber or thin disk lasers.

In laser welding according to the prior art, the penetration of the laser beam can vary along the welding seam, resulting in an irregular or rough welding seam. Accordingly, there is a need for improved methods and apparatus for laser welding.

SUMMARY OF THE INVENTION

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

According to one aspect of the invention, a laser processing apparatus comprises: at least one first laser device each providing a first laser beam to at least one first optical feed fiber; at least one second laser device each being at least one A second optical feed fiber provides a second laser beam; a tool for generating a composite laser beam comprising a first output laser beam and a second output laser beam for welding workpieces; wherein the first output laser beam has a circular cross-section, and the second output laser beam has an annular shape concentric with the first output laser beam. The second laser device is a fiber laser device or a fiber coupled laser device. The apparatus is configured to form a second output laser beam based at least on the second laser beam, and the second output laser beam includes a first wavelength and a second wavelength having a difference of at least 10 nanometers, or the second output laser beam has Spectral width of at least 10 nanometers.

According to a second aspect of the present invention, a method for welding a workpiece with a laser beam comprises the steps of:

- providing at least one first laser beam from at least one first optical feed fiber connected to at least one first laser device;

- providing at least one second laser beam from at least one second optical feed fiber connected to at least one first laser device;

- generating a composite laser beam comprising a first output laser beam and a second output laser beam for welding workpieces; wherein the first output laser beam has a circular cross-section and the second output laser beam has the same The concentric annular shape of the first output laser beam, the second output laser beam (2) is formed by a fiber laser device or a fiber-coupled laser device based at least on the second laser beam, the second output laser beam (2) comprises a The difference of 10 nanometers between the first wavelength and the second wavelength, or the second output laser beam (2), has a spectral width of at least 10 nanometers.

According to an embodiment, the wavelength of the second fiber laser output beam is 800-815 nm.

According to an embodiment, the first laser device comprises a fiber laser device and the second laser device comprises a fiber coupled diode laser device.

According to an embodiment, the laser processing device and the composite laser beam are suitable for welding aluminium sheets having a thickness between 1-20 mm.

According to an embodiment, a control unit functionally connected to the first and second laser devices is provided to individually control the power density in the first and/or second output laser beams.

Next, embodiments of the present invention are described in more detail with reference to the accompanying drawings.

Description of drawings

In the following, the present invention is described in detail with reference to the accompanying drawings, in which

Figures 1a and 1c illustrate an example of a laser welding operation according to some embodiments of the present invention;

Figure lb illustrates a cross-section of a composite laser beam according to some embodiments of the invention;

Figures 2a and 2b illustrate properties of a second output laser beam according to some embodiments of the present invention;

Figure 3 illustrates an optical arrangement for focusing a composite laser beam;

Figure 4 illustrates beam parameters related to Rayleigh length;

Figure 5 illustrates simulation results for focus shift;

Figure 6 illustrates a control unit for laser beam distribution power control in accordance with some embodiments of the present invention;

Figure 7 shows an example of an apparatus according to some embodiments of the invention;

Figure 8a shows a cross-section of a receiving end of a coupling tool according to some embodiments;

Figure 8b illustrates the refractive index profile at the output of a coupling tool according to some embodiments; and

Figure 9 schematically illustrates an optical component according to an embodiment.

Detailed ways

There is now provided a method and apparatus enabling improved weld quality. This is achieved by applying the specific compound laser beam configuration described further below.

Referring to Figure 1a, the present feature may be employed in a method and apparatus in which a first laser output beam 1 having a substantially circular cross-section and a first laser output beam 1 having a substantially annular shape concentric with the first laser output beam Two laser output beams 2 are applied from the laser processing head 3 to the part of the workpiece 4 to be welded. Thus, the first output laser beam 1 may be referred to as a circular or central beam, and the second output laser beam 2 may be referred to as an annular or annular beam.

The structure of the composite laser beam 7 emerging from the laser processing head 3 to the workpiece 4 is illustrated in FIG. 1 b. The annular outer annular beam 2 delivers the laser power provided by the second laser device. Correspondingly, the inner central beam 1 delivers the laser power provided by the first laser device.

In some embodiments, the central beam 1 is formed based on a laser beam from a fiber laser (device), and the ring beam 2 is formed by a fiber laser (device) or a fiber coupled laser (device). The central beam 1 and the annular beam 2 can be selectively directed to the components to be welded.

As illustrated in Figure 1c, the central beam 1 may be configured to induce a keyhole pattern in the workpiece. Between beams 1 and 2 is an annular shaped region 8 which provides only stray or no laser radiation at all.

A specific annular beam configuration is applied in the composite laser beam 7 to improve the welding quality. In some embodiments, the annular beam 2 comprises two beams 2a, 2b of different wavelengths. As further illustrated in Figure 2a, the annular beam 2 may comprise a first wavelength and a second wavelength having a difference of at least 10 nanometers, which may refer to the difference in mean wavelength. In some alternative embodiments, referring to Figure 2b, the annular beam 2 has a spectral width of at least 10 nanometers, which may refer to the overall spectral width of the annular beam 2, which may be determined by, in some embodiments, a One or more beams with different wavelengths are formed. Note that Figure 2b illustrates only one option for determining the spectral width, and the spectral width of the annular beam can be defined at higher intensity levels of the intensity peak. In further embodiments, the spectral width does not exceed 100 nm, and it may be selected in the region between 10 nm and 100 nm, such as 10-50 nm.

The present arrangement applying at least 10 nm difference in mean wavelength or at least 10 nm wide spectrum achieves a small variation in penetration depth along the beam path. This is illustrated by line 6 in Figure 1c, which has relatively little variation compared to line 5 provided without the specific annular beam configuration. In addition, the amount of spatter can be reduced and lower porosity can be achieved. Furthermore, an annular beam 2 with at least 10 nm difference in mean wavelength or at least 10 nm wide spectrum can be used to remove alumina from surfaces without deformation while welding aluminium and aluminium alloys. This method reduces the amount of alumina seal and provides better and stronger weld quality. Additionally, additional preparation for oxide removal prior to soldering can be avoided or reduced.

Specific composite laser beam configurations have been tested in ring beam 2 with different spectral widths. A spectral width of 10 nm was observed to provide significantly better weld quality and lower porosity than a spectral width of 5 nm. In an example configuration, the spectral width of the ring beam 2 of about 100 nm can be achieved by arranging four laser beam sources at 20 nm intervals (in the second laser device output), each laser beam source having a spectral width of 10 nm . For example, wavelengths in the region of 1030-1090 nm can be applied.

Referring to Figure 3, an optical system for laser beam transformation is illustrated. In at least some embodiments, such an optical system may be used in a laser processing head 3 for a compound laser beam 7 .

The focal lengths of the collimating and focusing lenses are f _col and f _foc , respectively, θ ₀ is the convergence angle, d ₀ is the beam diameter, and Z _R is the Rayleigh distance at the focal point on the workpiece.

其中M²为射束理想因子并且λ为射束的自由空间波长。The focus diameter depends on the divergence angle and on the beam parameter product (bpp) of the focused beam.

where ^M2 is the beam ideality factor and λ is the free space wavelength of the beam.

Figure 4 further illustrates beam parameters related to Rayleigh distance. The Rayleigh distance is a suitable scale for evaluating the focus shift Df for wavelengths with broad spectrum lasers due to dispersion of the refractive index of the material used in the optics of the processing head. The Rayleigh distance Z _R provides the focal length in which the laser beam is in focus. The parameter b=2Z _R can be described as the depth of focus. The Rayleigh distance of an ideal Gaussian laser beam is defined by the minimum beam radius w _at the focus and the wavelength λ:

For non-ideal or multimode laser beams, the Rayleigh distance is one-half ^M2 of the Rayleigh distance of an ideal Gaussian beam. When Df<< _ZR , changes in focus distance caused by different wavelengths of the beam may not have a significant effect on the quality of laser processing. On the other hand, when Df ~ Z _R or Df > Z _R , the width of the wavelength spectrum may have a significant effect on the laser welding quality. Note that the thickness of the processed material also affects the quality.

Figure 5 illustrates simulation results for focal shift due to dispersion of the refractive index of a single lens element made of fused silica. In this example, when laser welding is performed with a 250 mm focusing lens, a focal shift of 0.1 mm can be achieved with a wavelength difference of 15 nm between the first wavelength 2a and the second wavelength 2b of the second output laser beam. When using multiple lens elements as in a typical processing head, the focus shift due to dispersion will also increase compared to the case of a single element.

Power levels for fiber or fiber coupled lasers (devices) can be controlled from 0 to 10 kW or more, depending on the needs of the application in question. In many applications, fiber laser output power levels of about 1 to 4 kW for the ring beam 2 can be applied.

This particular composite beam configuration enables the application of lower power levels due to welding compared to when conventional laser beams are used. In an example embodiment, the laser power may be 600 W for center beam 1 and 1 kW for annular beam 2, with 100 mm/s welding speed for welding aluminum (example given for 3000 series aluminum). With these parameters, penetration depths of 1 mm and very good laser welding quality can be achieved.

By appropriately controlling the welding parameters of the central beam 1 and annular beam 2, the length of the melt pool of the laser welded seam can be optimized with this particular composite beam configuration. Splash can be significantly reduced by optimizing the length of the melt pool and minimizing turbulence within the melt pool. In addition, by optimizing the length of the melt pool, it is possible to give sufficient time for gases and bubbles to escape the melt before the melt solidifies. This promotes lower porosity and reduced number of voids in the welded seam.

In some embodiments, the wavelength of the fiber or fiber coupled laser in the ring beam 2 is in the region of 1030-1090 nm. The wavelength of the fiber laser in the central beam 1 can be chosen depending on the application in question, in some embodiments in the region of 700-1200 nm, such as eg 1070 nm.

In some embodiments, the laser processing device and composite laser beam are suitable for welding aluminum sheets. The aluminium plate may have a thickness between 1-20mm (preferably, 1-10nm). For example, the wavelength(s) of the annular beam 2 in the region of 800-1100 nm can be selected. The wavelength of 808 nm in the annular beam 2 makes it possible, due to the absorption peak at the wavelength of 808 nm, to obtain welding results of particularly good quality, at least when welding 6000 series aluminum alloy parts.

In some other embodiments, the second output laser beam 2 may comprise a fiber coupled diode laser beam. The addition of a suitable fiber-coupled diode laser beam in the ring beam 2 promotes an increase in the absorption of the optical power of the composite laser beam 7 .

In an embodiment, a combination of fiber and diode lasers is applied to form the annular beam 2 . For example, one of the light sources (of the second laser device or of the further third laser device) for the ring beam 2 can emit diode light. This makes it possible to further improve the stability of penetration depth, as also illustrated by line 6 in Fig. 1c, compared to line 5 provided without the diode laser device for the ring beam, said Line 6 has relatively little variation. In such an embodiment, beam 2a may refer to a fiber laser beam, and beam 2b may refer to a diode laser beam. In some embodiments, the wavelength of the diode laser beam is in the region of 0.5 to 1.5 μm in the ring beam. In some embodiments, diode laser output power levels in the range of 10 to 50 W are applied to the ring beam 2 . In some embodiments, the fiber and diode beams in the ring beam and their power levels can be adapted independently.

Accordingly, there are various advantages achievable by applying the presently disclosed features and applying added diode light for compound laser beam welding. One advantage is that weld seam quality and uniformity can be improved. The specific configuration of the diode light in combination with the fiber laser in the form of an annular ring achieves an improvement in weld quality. Furthermore, this enables spatter to be reduced since a more stable melt pool of the material being processed can be achieved.

Figure 6 illustrates a control unit 10 for controlling the generation of a central beam 1 and a ring beam 2 of a laser device according to some embodiments. The control unit 10 is directly or indirectly connected to at least one laser unit 12 adapted to generate the central beam 1 and/or the ring beam 2 . The control unit 10 may comprise a general purpose computer provided with suitable software for power control, or the control unit may comprise a microcontroller. The control unit includes at least one processor 11, which may be a single-core or multi-core processor, where a single-core processor includes one processing core and a multi-core processor includes more than one processing core. The processor may include at least one application specific integrated circuit ASIC. A processor may be a means for performing method steps in an apparatus. The processor may be configured, at least in part, by computer instructions to control the particular composite beam configuration and distribution(s) presently illustrated.

The control unit device may include a memory 13 . The memory may include random access memory and/or persistent memory. The memory may include at least one RAM chip. The memory may include, for example, solid state, magnetic, optical and/or holographic memory. The memory may be at least partially accessible to the processor. The memory may include computer instructions 14 which the processor 11 is configured to execute. When computer instructions configured to cause the processor to perform certain actions are stored in the memory, and the apparatus is generally configured to run under the direction of the processor using the computer instructions from the memory, the processor and/or at least one thereof The processing core may be considered to be configured to perform some of the described actions. The memory 11 may be included at least in part in the processor. The memory 11 may be at least partially external to the device, but accessible to the control unit device.

The presently illustrated features may be caused by at least one computer program stored in the memory 13 and comprising instructions which, when executed in the processor 11 cause the processor to pass corresponding A control signal is output to control the configuration of the laser beams 1, 2a, 2b. The memory 13 may also store various parameters 15 affecting the properties of the annular beam 2 and/or the central beam 1 controlled by the processor, such as defining different welding profiles and programs adjustable by the operator and different central and/or A set of parameters for ring beam parameters.

The control unit device may include a user interface UI 16 . The UI may include, for example, at least one of a display, a keyboard, a touch screen. The control unit may be arranged to control the laser beam configuration and/or parameters based at least in part on user input. The control unit 10 may also be connected to one or more sensors 17, such as sensors monitoring the progress of the laser welding operation and/or sensors detecting properties of the workpiece being processed. The control unit 10 may also include other units such as transmitters and receivers configured to transmit and receive information according to at least one cellular or non-cellular standard.

According to some embodiments, the control unit 10 may be configured to control the power density in the central beam 1 and/or the annular beam 2 individually, regardless of the state of the other beam. The relationship between the power density of the central beam 1 and the power density of the annular beam 2 can be controlled according to the thickness of the workpiece to be welded. For example, the control unit 10 may be configured to cut off the ring beam in response to the thickness of the workpiece falling below a predetermined thickness limit for interrupting the ring laser beam. In some embodiments, the limit value is selected from the range of 4 to 8 mm, in one embodiment 6 mm. The different power densities and relationships between the central beam 1 and the annular beam 2 can be controlled depending on the material being welded.

There are also other welding parameters that can be controlled by the control unit 10 . Some examples of such parameters include, but are not limited to, welding progress speed, diameter of the central beam and/or annular beam, modulation on/off, modulation parameters, and other beam properties.

Embodiments are applicable to spot welding and continuous welding applications. In the case of continuous welding, the leading edge of the annular beam 2 in the direction of movement of the laser treatment head causes a first intensity peak, and the trailing edge of the annular beam 2 causes a second intensity peak. Thus, the element is heated in stages, and the intensity levels at the trailing and leading edges may be lower compared to a single spot beam to induce sufficient melting. In addition to preheating, the leading edge provides contaminant ablation. This makes it possible to avoid abrupt temperature changes, and avoid or at least reduce subsequent tempering, and thus avoid or at least reduce weak areas caused by abrupt temperature changes. The use of annular beams in continuous welding is also advantageous in avoiding spatter. In an embodiment, the power density of the central beam 1 may be set low, or the central beam may even be completely closed. Overheating can thus be avoided.

Composite laser beam 7 (i.e. a mixture of center beam 1 and ring beam 2) can be generated by combining laser beams from the originating laser device and the feed fiber in a multicore optical fiber, using center beam 1 and ring beam 2. The resulting composite laser beam of beam 2 can be directed therefrom to the workpiece. The first optical feed fiber may be aligned with the first core of the multi-core optical fiber, and the second optical feed fiber may be aligned with the second core of the multi-core optical fiber. The first core of the multi-core optical fiber has a circular cross-section, and the second core has an annular shape concentric with the first core. Some additional example embodiments are described below.

In some embodiments, referring also to the illustration of Figure lc, keyhole laser welding is applied in combination with thermal conduction welding to provide dynamically adaptable center and ring laser beam distributions. Thermal conduction welding is suitable for welding metal sheets with material thicknesses typically up to about 2 mm. A metal sheet processed by a laser capable of conduction welding strikes a relatively shallow but wide spot of the metal. Typical keyhole patterns are caused by high brightness lasers such as fiber lasers. The diameter of the keyholes may be in the region of less than one millimeter, such as 0.1 millimeters, and the diameter of the dots may be in the region of several millimeters, such as, for example, 3 millimeters. When comparing the application of pure keyhole welding and hybrid welding by circular and annular laser beams, it has been noted that hybrid welding penetrates at least 20% deeper than pure keyhole welding using the same processing speed.

Figure 7 shows one embodiment of an apparatus to achieve independent center beam and ring beam power control, and in which and by which the above-described features on specific composite laser beam configurations may be applied of at least some. A first laser (device) 30 is connected to a laser beam combiner 34 with an optical feed fiber 32 . Likewise, one or several second lasers 31 and feed fibers 33 are connected to a beam combiner 34 . The task of the combiner is to arrange all the incoming laser beams so that they can be coupled to the twin-core optical fiber 35 . Thus, the hybrid nature of the laser device is the result of having two laser beams propagating inside a single dual core optical fiber 35 . The two laser beams inside the fiber 35 typically have different brightness and intensity distributions, and may have different wavelengths. Furthermore, the power levels in the two laser beams can be independently and continuously controlled by adjusting the power levels from the first laser 30 and the second laser device 31 .

To achieve sufficient beam brightness, the first laser device 30 may be a high brightness fiber laser comprising a diode-pumped single or multiple fiber laser oscillator or master oscillator-power amplifier (MOPA) modules, each of which is For example, it consists of a fiber-coupled diode laser coupled to a fiber-optic resonator. Additional examples of high brightness lasers are fiber coupled thin disk lasers or Nd-YAG lasers, which utilize optical pumping from diode lasers. Modern laser technology often relies on light as the energy transfer medium because many active solid-state light-amplifying materials are insulators. Diode lasers have replaced previously used flash lamps as energy pumps due to their higher efficiency and narrower spectrum.

The second laser device 31 may be configured to provide a specific second laser beam(s) for forming the annular beam 2 configuration as illustrated above. The second laser device 31 may be a fiber laser or a fiber coupled laser, which may also comprise a solid state laser resonator pumped by a diode laser, eg a thin disk laser resonator (not shown). As illustrated in Figure 8a, a dual-core optical fiber 35 may be arranged to transmit the laser beam from the first laser device 30 in its central core and arranged annularly around the central core at a distance from the central core The beams generated by one or more second laser devices 31 are transmitted in the outer core of the .

In some embodiments, both the first and second laser devices 30, 31 are fiber lasers, each having independently controllable power levels. Some lasers are fiber lasers by construction and inherently feed light into an optical fiber; other lasers require optical interfacing with fiber optics in order to align the laser beam to the core of the output fiber. The purpose of the laser arrangement and the power ratings and other properties of the individual laser modules determine which types of lasers are feasible to connect to the beam combiner 34 .

In some embodiments, the apparatus includes additional diode laser equipment (not shown) that provides a diode laser beam to beam combiner 34 . The beam combiner 34 is adapted to align the diode laser beam with at least one second core of the multi-core optical fiber.

The dual-core optical fiber is connected at its opposite ends to a laser processing head 20 which directs the combined or compound laser beam 7 forward to the workpiece 21 . Laser processing head 20 typically includes collimating and focusing lenses to produce an image of the intensity distribution exiting the end of optical fiber 35 onto workpiece 21 having a desired size as determined by the focal length of the lenses. The task of the laser head 20 may also be to provide a jet of pressurized gas to the welding line. Pressurized gas may also be applied to further protect the optics within the laser head 20 from splattered molten metal, and also to remove splattered molten metal from the weld line to help keep the weld line clean. In one embodiment, at least the welding progress turning points are applied in conjunction with an oxygen assist gas to provide additional energy and enable further improvement of the weld edge quality in these points.

In one embodiment of the invention, the device is provided with a control unit, such as the control unit 10 illustrated above. The control unit can also be integrated in one of the laser devices 30 or 31 . Alternatively, for convenience and reliability, all units 30, 31 and 10 may be placed in a single housing and integrated with each other in their construction. As indicated, the control unit 10 can be used to perform independent power control of the distribution of the annular beam 2 and the central beam 1, and to implement a dynamically adjustable annular central beam, which can be achieved by applying the features described above. At least some of it comes with on-the-fly adjustments. The control unit may be configured to control modulation and/or other parameters of at least one of the laser devices 30 , 31 . Preferably, the modulation of the two laser beams can be dynamically controlled separately. Thus, with the same device, a wide variety of different welding applications and purposes are possible. The beam distribution can be dynamically adjusted to suit the various needs of challenging welding types/applications, such as different materials, coatings and/or thicknesses.

The control unit 10 may be arranged to receive feedback 36 from a user of the laser head 20, or automatic feedback eg from a light intensity sensor. The feedback or input is then used to control the power of the lasers 30 and 31 to follow predetermined targets, or to adjust the laser power based on the resulting welding results observed at the workpiece 21 . The control unit 10 or another control unit may also control other functions of the apparatus, such as the movement of the laser processing head 20 relative to the workpiece.

In accordance with the present invention, the beam combiner 34 is made of fused silica components, wherein optical power is propagated inside the fused silica through the entire combiner structure, and the combiner has optical fibers at the input and output. Therefore, in the present invention, the beam combiner 34 may be referred to as an all-glass fiber combiner.

A cross-section of an example dual/multi-core optical fiber 50 with a central core 51 with a primary cladding 54 is shown in Figure 8a. The outer core 53 is spatially formed by the inner clad 54 and the outer clad 55 . As will be clear to those skilled in the art, the cladding is defined as a material having a lower refractive index than that of the core. For example, the diameter of the central core 51 may be 70 µm, and the inner and outer diameters of the outer core 53 may be 100 µm and 180 µm, respectively. The central core 51 and the peripheral core 53 may also take other forms than those described above. The central core 51 may be, for example, square or rectangular in shape. The peripheral core 53 may also have a rectangular border or be composed of multiple linear or circular shaped segments.

Shown with dashed lines is how the cores of the ends of the fusion feed fibers 56 and 57 (fibers 72 and 71 in FIG. 9 ) from the beam combiner can align with the cross-section of the twin-core optical fiber 50 . For example, each of the four feed fibers 57 aligned with the peripheral core 53 (for forming the annular beam 2 ) may have a spectral width of 10 nm at 20 nm intervals, resulting in a total of about 100 nm for the annular beam 2 spectral width.

The laser radiation in the central core 51 of the dual-core optical fiber 50 has a central and narrow spatial intensity distribution, while the state of the intensity distribution in the outer core 53 takes the shape of a donut. This spatial intensity pattern is further imaged onto the workpiece using processing optics in the laser head 20 . With this configuration, the beam quality of the laser beam is relatively high in both the central core and the outer core.

Referring now to FIG. 8b, an example refractive index profile of the optical twin core fiber 50 is shown. Cores 51 and 53 have refractive indices n ₅₁ and n ₅₃ that are higher than the refractive indices n ₅₄ and n ₅₅ of surrounding materials 54 and 55 , respectively. In this way, the laser beam is directed to the workpiece where degradation in the annular intensity distribution and optical power and intensity in each of the cores is least likely.

The refractive index of fused silica can be adjusted by doping with impurities. Doping the fused silica with germanium results in an increase in the refractive index, while doping the fused silica with fluorine results in a decrease in the refractive index. Thus, for example, cores 51 and 53 may be made of Ge-doped or undoped fused silica, and their main claddings 54 and 55 may be made of F-doped fused silica.

Shown in FIG. 9 are key optical components 70 of fiber combiner 34 . It is a porous capillary with a main body portion consisting of a fused silica glass tube 77 for receiving from at least two laser devices laser beams (not shown) delivered by optical feed fibers 71 and 72 Inputs 76 (eg, fibers 32 and 33 from devices 30 and 31). It also has opposite output ends 74 for delivering a composite output laser beam consisting of at least two laser beams aligned with each other in the same direction.

The optical feed fibers 71, 72 entering at the input end 76 extend through the body portion in the capillary to the output end 74 and are fused with the glass tube 77 to form a component consisting of light guiding cores 71a, 72a and surrounding glass material. The core has an index of refraction higher than the index of refraction of the surrounding glass material surrounding the core to provide propagation of optical power through the entire component in the core by total internal reflection.

To illustrate the principles of the fiber combiner, the dimensions of the cores and the dimensions of the components 70 are not to scale, and for clarity only one pair of cores are shown with dashed lines.

The optical component 70 may be manufactured, for example, by drawing. In this example, there may be a larger hole for fiber 72 that is about 300 μm in diameter in the center, and may exist for fiber 71 that is placed symmetrically with and around the center hole 72 Four smaller holes. Smaller pores may have a diameter of, for example, about 150 μm. The outer diameter of the capillary can be, for example, 1 mm. The material of the tube can be, for example, fused silica. The optical fiber, whose outer cladding of bulk glass (not shown) has preferably been at least partially etched away, is inserted into the intermediate hole and passed through the waist portion 73 of the capillary cone. When the fiber is in place, the capillary 70 is heated at the waist section 73 to fuse the fiber to the tube and to form a first central light guiding core 72a and a second light guiding core 71a, which all extend through the optical component 70 .

Alternatively, the optical fibers 71, 72 may have an inner core of pure fused silica material and an outer clad of F-doped fused silica. In this manner, the fused silica glass tube 77 of the optical component 70 can be made of pure fused silica, since the optical fiber's light-guiding core is inherently surrounded by a material having a lower refractive index. This means that the light remains in the cores 71a, 72a even if the index of refraction of the capillary is the same as that in the core of the fiber. In this case, the outer fiber cladding of the bulk glass can be etched away until the F-doped cladding, or even further, as long as some F-doped cladding remains in the pure or Ge-doped inner fiber core around.

The molten cores 71a , 72a (shown in phantom) and the tube 70 are then cut or split to create the end surface 74 . Then, a duplex fiber 35 similar to the one shown in FIG. 8 can be welded to the capillary at end 74 to form a weld 75 .

In a preferred embodiment, the center of the first optical feed fiber 72 is aligned with the center of the component 70, and the centers of, for example, four second optical feed fibers 71 are positioned at a predetermined distance R from the first central light guide core 72a An output beam is provided at output 74 . It will be appreciated that the number of second feed fibers is not so limited, but instead, for example, 8, 16 or 32 instead of 4. The second light guiding cores 71a are preferably arranged symmetrically with respect to the central core 72a to provide output beams having an angular distance of 90° from each other.

The presently disclosed laser welding methods and apparatus can be used in a wide variety of applications. Particular advantages are realized in applications where it is required to achieve excellent weld surface quality of laser welding materials with different properties such as thickness and/or variation and multi-modal welding operations. A single welding device can now be used for these changing properties/requirements, thereby enabling the optimum welding beam distribution to be adapted immediately accordingly. As some examples, the present system may be particularly advantageous for the welding needs of the automotive industry.

It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures, process steps or materials disclosed herein, but extend to equivalents thereof that one of ordinary skill in the relevant art would recognize. It is also to be understood that the terminology employed herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

Various embodiments and examples of the invention may be referred to herein along with alternatives for the various components thereof. It is to be understood that such embodiments, examples and alternatives are not to be construed as de facto equivalents of each other, but are to be considered separate and autonomous representations of the invention.

Furthermore, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. Numerous specific details (such as examples of lengths, widths, shapes, etc.) are provided in the description to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been described or shown in detail so as not to obscure aspects of the invention.

While the foregoing examples illustrate the principles of the invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that, without exercising the ability of the invention, and without departing from the principles and concepts of the invention Below, many modifications may be made in the form, use and details of the embodiments. Accordingly, the invention is not intended to be limited except as by the claims set forth below.

Claims (10)

1. A laser welding apparatus comprising:

-at least one first laser device (30) each providing at least one first optical feed fiber (32) with a first laser beam;

-at least one second laser device (31) each providing at least one second optical feed fiber (33) with a second laser beam;

-a tool for generating a composite laser beam (7) comprising a first and a second output laser beam (1, 2) for welding a workpiece (21); wherein the first output laser beam (1) has a circular cross-section and the second output laser beam (2) has a ring-like shape concentric with the first output laser beam (1),

the second laser device (31) is a fiber laser device or a fiber coupled laser device,

the device is configured to form the second output laser beam (2) based at least on the second laser beam, and

the second output laser beam (2) comprises a first wavelength and a second wavelength having a difference of at least 10 nanometers, or

The second output laser beam (2) has a spectral width of at least 10 nm.

2. The laser welding device according to claim 1, wherein the wavelength of the second fiber laser output beam (2) is 800-815 nm.

3. The laser welding apparatus according to claim 1, wherein the apparatus comprises a control unit (10), the control unit (10) being functionally connected to the first laser device (30) and the second laser device (31) to individually control the power density in the first and/or second output laser beams (1, 2).

4. The laser welding apparatus according to any preceding claim, wherein the means for generating the composite laser beam comprises:

-a beam combining tool (34) connected to the first and second feeding fibers (32, 33) and to a multi-core optical fiber (35, 50, 70), the combining tool (34) being adapted to form the composite laser beam (7) by aligning the at least one first optical feeding fiber (72, 56) with a first core (51) of the multi-core optical fiber (50) and the at least one second optical feeding fiber (71, 57) with at least one second core (53) of the multi-core optical fiber (50), and

-said first and second cores (51, 53) are connectable to a laser processing head (20) for directing said composite laser beam (7) to said workpiece (21).

5. The laser welding apparatus according to any preceding claim, wherein the first laser device (30) comprises a fiber laser device and the second laser device (31) comprises a fiber coupled diode laser device.

6. The laser welding device according to any preceding claim, wherein the laser processing device (36) and the composite laser beam (7) are adapted to weld aluminium sheets having a thickness between 1-20 mm.

7. The laser welding apparatus according to any preceding claim, wherein the spectral width of the second output laser beam (2) is less than 100 nanometers.

8. The laser welding device according to any of the preceding claims, wherein the wavelength(s) of the annular beam (2) are in the region of 800-.

9. A method for welding a workpiece with a laser beam, comprising:

-providing at least one first laser beam (1) from at least one first optical feed fiber (32) connected to at least one first laser device (30);

-providing at least one first laser beam (2) from at least one second optical feed (33) fiber connected to at least one first laser device (31);

-generating a composite laser beam (7) comprising a first and a second output laser beam (1, 2) for welding a workpiece (21); wherein the first output laser beam (1) has a circular cross-section and the second output laser beam (2) has a ring-like shape concentric with the first output laser beam,

the second output laser beam (2) is formed by a fiber laser device or a fiber coupled laser device based on at least the second laser beam, and

the second output laser beam (2) comprises a first wavelength and a second wavelength having a difference of at least 10 nanometers, or

The second output laser beam (2) has a spectral width of at least 10 nm.

10. The method according to claim 9, wherein the power densities in the first and second output beams (1, 2) are individually controlled by a control unit (10), the control unit (10) being functionally connected to the first and/or second laser device (30, 31).

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